Optical identification of silicon as a shallow donor in MOVPE grown homoepitaxial AlN

摘要

Aluminum nitride (AlN) layers doped intentionally withdifferent concentrations of silicon atoms acting as shallowdonors were grown by MOVPE on bulk c-plane AlN tominimize dislocations in the doped layers; typical values for thedislocation density in the bulk AlN substrates are less than104 cm~(-2). The actual silicon concentration was confirmed bysecondary ion mass spectroscopy (SIMS) analysis and rangingfrom 1017 to 1019 cm~(-3). In highly resolved low temperaturephotoluminescence (PL) investigations, we found dominatingbandgap-related sharp emission lines with linewidth lower than500 meV for undoped samples. We tentatively assign silicon asthe shallow donor causing the bound exciton line with 28.5 meVexciton localization energy, for which we found an intensityratio relative to the free exciton line being linearly dependenton the silicon concentration. For increasing Si content, therespective emission band also broadened asymmetrically andshifted to lower energies as expected from the analogy withother semiconductor systems.